Immune Dysfunction as Measured by the Systemic Immune-Inflammation Index is Associated with the Sub-Type of Minimal Residual Disease and Outcome in Stage II Colon Cancer Treated with Surgery alone

Within 5 years after curative surgery for stage II colon cancer 25% of patients will relapse due to minimal residual disease (MRD). MRD is the net result of the biological properties of subpopulations of primary tumour cells which enable them to disseminate, implant in distant tissues and survive and the immune system's ability to eliminate them. We hypothesize that markers of immune dysfunction such as the systemic inflammation index (SII) are associated with the sub-type of MRD defined by bone marrow micro-metastasis (mM) and circulating tumour cells (CTCs). A higher immune dysfunction being associated with a more aggressive MRD and worse prognosis. Blood and bone marrow samples were taken to detect CTCs and mM using immunocytochemistry with anti-CEA one month after surgery. The SII, absolute neutrophil, platelet and lymphocyte counts (ANC, APC, ALC) were determined immediately pre-surgery and one month post-surgery. These were compared with the sub-types of MRD; Group I MRD (-); Group II mM positive and Group III CTC positive; cut-off values of SII of >700 and >900 were used. Follow-up was for up to 5 years or relapse and survival curves using Kaplan-Meier (KM) were calculated. One hundred and eighty one patients (99 women) participated, mean age 68 years, median follow up 4.04 years; I: = 105 patients, II: N= 36 patients, III: N=40 patients. The SII significantly decreased post-surgery only in Group I patients. The frequency of SII >700 and >900 was significantly higher in Group III, between Groups I and II there was no significant difference. The SII was significantly associated with the number of CTCs detected. The 5-year KM was 98% Group I, 68% Group II and 7% Group III. The results of the study suggest that the severity of immune dysfunction as determined by the SII is associated with differing sub-types of MRD and a worse prognosis; increasing immune dysfunction is associated with a more aggressive CTC positive MRD sub-type; a more severe immune dysfunction is associated with a higher number of CTCs detected. .